1. Field of the Invention
The present invention relates to an internal combustion engine control device which determines the combustion state in the internal combustion engine on the basis of ion current value detected from a cylinder after combustion, so as to set control parameters of the internal combustion engine according the determined combustion state. More particularly, the invention relates to an internal combustion engine control device which feedback-controls control parameters according to the determination results of the ion current value, thereby improving the combustion state in the internal combustion engine without increasing the cost.
2. Description of the Related Art
FIG. 3 is a block diagram showing the construction of a conventional internal combustion engine control device. Such a control device is applied to only some high-grade automobiles.
Referring to FIG. 3, the conventional internal combustion engine control device comprises: angle detection means 10 which is formed of, for example, a rotation plate and is synchronized with the rotation of the internal combustion engine so as to generate a pulsating reference position signal T.theta. for indicating the reference position of each of the cylinders in correspondence with a predetermined crank angle; various kinds of sensors 20 for detecting the drive state D indicative of a load to an internal combustion engine, such as the air flow rate (throttling rate), rotation number, suction temperature, and the like; ion current detection means 30 for detecting the ions produced by the combustion of the cylinders so as to generate the ion current value I; cylinder internal pressure sensor 40 provided for each of the cylinders so as to detect the cylinder internal pressure Pc; and control means 50 including a microcomputer, and the like.
The angle detection means 10 for generating the reference position signal T.theta. is provided for a crank shaft or a cam shaft of an internal combustion engine so that the reference position signal T.theta. indicates a predetermined reference position corresponding to the crank angle (the rotation angle of the crank shaft). The reference position is used as the reference of the timer control for the control parameters of the ignition timing, or the like, and is generally set to be, for example, B75.degree. (75.degree. before the top dead center) and B5.degree., etc.
The ion current detection means 30 for detecting failures, for example, a misfire, of an internal combustion engine is provided for all or certain cylinders according to the necessity.
Referring to FIG. 3, the control means 50 comprises a control parameter setting section 60 for calculating control parameters of the ignition timing, or the like, for each of the cylinders on the basis of the reference position signal T.theta. and the drive state D and calculated varying the control parameters according to the cylinder internal pressure Pc so as to output the resultant control parameters Ta; and an ion current determining section 70 for comparing the ion current value I with the reference level according to the reference position signal T.theta. and determining the combustion state, such as a misfire, in an internal combustion engine so as to output a determining signal C.
The control parameter setting section 60 produces control parameters Ta indicative of, for example, the control duration, corresponding to the ignition timing, and also executes the following processes. For example, when the determining signal C indicates a misfire, the control parameter setting section 60 executes a misfire inhibiting process on the targeted misfiring cylinder by means of increasing the ignition power supply capacity, or the like, and also executes a process for inhibiting the discharge of the unburned gas caused by fuel injection stoppage. The control parameter setting section 60 further varies the calculated control parameters according to the cylinder internal pressure Pc so that the combustion state is optimal, thereby outputting the resultant control parameters Ta. The control parameters Ta comprise various elements such as not only ignition timing, but also fuel injection timing, the duration for supplying the power to an ignition coil.
FIG. 4 shows the schematic construction of the internal combustion engine and is also a circuit diagram indicating the ion current detection means 30 shown in FIG. 3.
Referring to FIG. 4, the internal combustion engine comprises an ignition coil 81 having a primary winding 81a and a secondary winding 81b; a power transistor 82 for cutting off the current i1 supplied to the primary winding 81a by the ignition pulse P corresponding to the ignition timing; and an ignition plug 83 discharged by a high voltage which generates in the secondary winding 81b.
The ion current detection means 30 comprises a DC power supply 31 having a voltage of a range from 100 V to 200 V for discharging ions, which is used as the ion current i, produced by discharge explosion in the ignition plug 83; a resistor 32 connected in series to the DC power supply 31 for converting the ion current i into a voltage signal; an output terminal 33 for outputting the detected value I of the ion current i as a voltage signal; and a reverse-current preventing diode 34 connected parallel to the DC power supply 31 and the resistor 32.
The output terminal 33 for outputting the ion current value I is connected to the ion current determining section 70 of the control means 50 through a wave-form shaping circuit (not shown).
If the discharge explosion fails to be performed due to a misfire of a cylinder which is to be controlled in the ignition cycle, an abnormal explosion referred to as afterburning is caused after the ignition cycle, thereby damaging the cylinders or injuring the catalyst used for disposing the exhaust gas due to exhausting the unburned gas. Thus, it is necessary to detect the combustion state in each of the cylinders, and when a misfire is detected, for example, it is necessary to take various measures to avoid further misfires in order to protect the internal combustion engine.
In view of the above background, a conventional internal combustion engine control device includes the ion current detection means 30 for detecting ions produced in a cylinder in which the fuel is burning as the ion current i. However, the ion current value I from the ion current detection means 30 can be used only for determining whether a misfire has occurred and for identifying in which cylinder the fuel is burning.
Also, in order to maintain the optimal combustion state in the internal combustion engine, it is necessary, for example, to set the ignition timing to match the optimal crank angle according to the drive state and to control the fuel injection volume so that the air fuel ratio is equal to the theoretic mixture ratio (14.7). If the control parameters Ta of the ignition timing, the fuel injection volume, and the like, are set by the above open loop control, the optimal combustion state cannot be reliably maintained.
In order to overcome the above drawback, a conventional internal combustion engine control device includes an cylinder internal pressure sensor 40 for detecting the cylinder internal pressure Pc of the cylinder in which the fuel is burning. The control parameter setting section 60 varies the control parameters Ta according to the fed-back cylinder internal pressure Pc in the course of burning so that the combustion state is optimal. However, the cylinder internal pressure sensor 40 is expensive, thus increasing the cost.
The operation of the conventional internal combustion engine control device will now be described with reference to FIGS. 3-5.
FIG. 5 shows a wave form indicative of the ion current i and the ignition pulse P in which the primary current I1 of the ignition coil 81 is cut off by the ignition pulse P so as to cause a discharge explosion in the ignition plug 83 which is ignited, thus increasing the ion current i as the flame grows.
In general, the control parameter setting section 60 controls, for example, the ignition timing by the following process. It sets the rising and falling timings of the pulsating reference position signal T.theta. as the reference position and also finds the optimal ignition timing according to the drive state D with reference to the values in the map, thus calculating the control duration starting from the reference position to the ignition timing used as the control parameter Ta. The above map comprising the ignition timing data corresponding to the drive state D is obtained by experiment or other means in advance and stored in a memory (not shown) of the control means 50.
The ion current determining section 70 identifies the combustion state in each of the cylinders in the ignition cycle on the basis of the reference position signal T.theta. from the angle detection means 10 and the ion current value I from the ion current detection means 30, and when the ion current value I in the explosion process is smaller than the threshold value, for example, the ion current determining section 70 generates a determining signal C indicating that a misfire has occurred in the targeted cylinder.
When such a determining signal C is input, the control parameter setting section 60 varies the control parameter Ta so that the targeted cylinder can be inhibited from misfiring.
More specifically, the conventional internal combustion engine control device increases the ignition energy, in other words, increases the duration for supplying the primary current I1 to the ignition coil 81, so as to ensure the ignition of the ignition plug 83, or it makes the air fuel mixture rich or lean by increasing or decreasing the fuel injection duration, respectively, thereby confirming whether it is possible to avoid a misfire by such means of adjusting the ratio of the air fuel mixture. Further, if such a misfire state is not improved by varying the control parameter Ta which is targeted for avoiding misfires, the fuel injection to the misfiring cylinder is stopped, thereby preventing the unburned gas from being exhausted.
Ignition is performed in the cylinders by the following general process. When the power transistor 82 is cut off by the ignition pulse P, the negative-polar high voltage is applied to the ignition plug 83 connected to the secondary winding 81b so as to cause the discharging across the electrodes of the ignition plug 83, thereby igniting the air fuel mixture. Such an ignition further brings about the explosive combustion so as to produce ions in the exploded cylinder due to the ionization tendency. At the same time, a biasing voltage of the DC power supply 31 is applied to the electrodes of the ignition plug 83 which have already been discharged, and consequently, such electrodes serve the function of detecting the ion current i.
The resultant ions in the cylinder flow as the ion current i by the positive-polar biasing of the DC power supply 31 and such an ion current i is converted into the detected value I by the resistor 32 so as to be output from the output terminal 33. As a result, the ion current determining section 70 simply refers to a pulse obtained by wave-form shaping the ion current value I of the pealhold value or the ion current value I greater than the threshold value, thereby determining whether the cylinder in the ignition cycle are reliably ignited.
Since the level of the ion current value I varies depending upon the reference position signal T.theta., a threshold value for comparison for detecting a misfire is also appropriately varied in accordance with the reference position signal T.theta..
It is not possible to determine the correct combustion state from only the ion current value I, for example, the peak value of the ion current value I, and thus, the suitable control parameters Ta cannot be set.
A description will now be given in detail of the ion relationship between the control parameters Ta and the current value I with reference to FIGS. 6-8.
FIG. 6 shows typical wave forms indicating peak values and pulse widths of the ion current values. I indicates the ion current values in the good combustion state and in the failed combustion state indicated by the solid line and one-dot chain line, respectively. FIG. 6 also indicates a threshold value TH, a peak value IP and a pulse width IW.
FIG. 7 is a characteristics diagram indicating the pulse width IW and the peak value IP with respect to the air fuel ratio. As is seen from FIG. 7, the peak value IP shows its maximum with respect to the theoretic mixture ratio (14.7), but the ion current value I is superimposed on a noise component and the peak value IP is thus, for example, erroneously detected. As a result, the maximum of the peak value IP tends to be varied, thus lowering the reliability. The pulse width IW also shows its maximum with respect to the theoretic mixture ratio, but is inclined to soar again when the air fuel ratio is lean.
FIG. 8 is a characteristics diagram indicating the pulse width IW with respect to the ignition timing. As is seen from FIG. 8, the pulse width IW substantially shows its maximum with respect to the optimal ignition timing MBT, but is inclined to soar again due to knocking, or the like, when the ignition timing is more advanced.
As can be clearly understood from FIGS. 7 and 8, with respect to the controls of the air fuel ratio and ignition timing, it is difficult to vary the control parameters Ta by the closed-loop control from only either the peak value IP or the pulse width IW of the ion current value I.
Therefore, the cylinder internal pressure sensor 40 is provided for each of the cylinders, thereby varying the control parameters by the closed loop control according to the cylinder internal pressure Pc. As stated above, however, the cylinder internal pressure sensor 40 increases the cost.
As described above, the conventional internal combustion engine control device uses the ion current detection means 30 and determines the combustion state the basis of either the peak value IF or the pulse width IW of the ion current detection value I. Thus, although the control device is capable of determining failures such as a misfire, it cannot identify the specific combustion states, for example, the theoretic mixture ratio, thus failing to vary the control parameters by the closed-loop control.
The above problem can be solved by using the cylinder internal pressure sensors 40 so as to detect the specific combustion states, such as the air fuel ratio, of an internal combustion engine but such a method results in an increase in the cost.